Positive dispense verification sensor

ABSTRACT

Systems and methods for positive dispense verification. In one aspect, a system has a plurality of light emitters. The light from the emitters is directed toward a plurality of light detectors across a proximately horizontal plane. The liquid dispense device is positioned above the horizontal plane of light emission from the plurality of light emitters to the plurality of light detectors such that the dispensed liquid will travel through the horizontal plane defined by the emitted light and onto the container being inoculated. Each of the plurality of detectors is coupled to an amplifier. The amplifier generates a signal in response to an interrupt in the transmission of light from the light emitters to the light detectors when the light path is disrupted by the dispense of liquid confirming the liquid was dispensed onto the container.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. patent application Ser. No.16/344,632, filed Apr. 24, 2019, allowed, which application is anational phase entry under 35 U.S.C. § 371 of International ApplicationNo. PCT/US2017/058567, filed Oct. 26, 2017, published in English, whichclaims the benefit of U.S. Provisional Application No. 62/414,113, whichwas filed on Oct. 28, 2016, all of which are incorporated herein byreference.

TECHNICAL FIELD

The present invention relates to systems and methods for verifying whena dispensing device, such as a pipette, has successfully dispensed asample into a container or slide.

BACKGROUND OF THE INVENTION

Various systems exist to streamline and increase efficiency forinoculation and testing of samples. To inoculate a sample container, apipette is often used to dispense the sample into the container. Toensure that a positive dispense or lack thereof is correctly detected,several techniques are known, such as vision systems and pressuremonitoring methods. In vision systems, a camera is sometimes used tocapture a drop of a sample. To detect a positive dispense accurately,complex image processing and analysis are often required. In pressuremonitoring systems, a sensitive pressure transducer is built in apipetting channel such that it can detect the pressure change during adispense. However, for pressure systems in particular, no existingpressure transducers are capable of detecting the distinction between adroplet clinging to a tip of a pipette and a droplet that has dispensedfrom the pipette. Moreover, vision, pressure and other existingtechniques are expensive, consume a great deal of physical space, lackreliability or have a combination of these limitations. These challengesbecome more pronounced as sample (i.e., droplet) sizes become smaller.

Thus, there is a need for improved systems and methods for accuratepositive dispense verification of liquids.

BRIEF SUMMARY OF THE INVENTION

Systems and methods for positive dispense verification are disclosed. Inone embodiment, a system has a plurality of light emitters. The lightfrom the emitters is directed toward a plurality of light detectorsacross a proximately horizontal plane. “Proximately horizontal” as usedherein refers to orientation of the light curtain relative to a planedefined by a surface onto which a liquid dispense device will dispenseliquid. However, the light curtain is not required to be parallel to thesurface onto which the liquid will be dispensed. The liquid dispensedevice is positioned above the horizontal plane of light emission fromthe plurality of light emitters to the plurality of light detectors suchthat the dispensed liquid will travel through the horizontal planedefined by the emitted light and onto the container being inoculated.Each of the plurality of detectors is coupled to an amplifier. Theamplifier generates a signal in response to an interrupt in thetransmission of light from the light emitters to the light detectorswhen the light path is disrupted by the dispense of liquid confirmingthe liquid was dispensed onto the container.

One aspect of the present disclosure relates to a system for positivedispense verification, the system comprising: a plurality of lightdetectors; a plurality of light emitters, wherein light transmitted fromthe light emitters is directed toward the plurality of light detectors;a liquid dispense device positioned above a light curtain defined by thelight directed from the plurality of light emitters toward the pluralityof light detectors such that liquid dispensed from the liquid dispensedevice will travel through the light curtain; and an amplifiercommunicatively coupled to the plurality of light detectors, wherein theamplifier generates a signal in response to an interrupt in atransmission of light from the plurality of light emitters to theplurality of light detectors.

In some embodiments, the light curtain is proximately horizontal inrelation to a surface onto which the liquid dispense device willdispense liquid. In some embodiments, the light curtain is proximatelyparallel to a surface onto which the liquid dispense device willdispense liquid. In some embodiments, the plurality of light emitterstransmit light between 800 nm and 900 nm. In some embodiments, theplurality of light detectors has approximately the same dimensions asthe plurality of light emitters. In some embodiments, the plurality oflight emitters includes an array of light emitters that are distributedin a row and spaced approximately equidistant from one another. In someembodiments, the plurality of light emitters includes a plurality ofarrays of light emitters that are distributed in rows.

In some embodiments, a space between the liquid dispense device and thelight curtain is such that a drop of liquid having a volume of at leastten microliters will span the space. In some embodiments, a droplet ofthree microliters of liquid dispensed from the liquid dispense devicecauses the amplifier to generate a signal in response to an interrupt ina transmission of light from the plurality of light emitters to theplurality of light detectors. In some embodiments, the light curtain hasno gaps that would allow a droplet of three or more microliters ofliquid dispensed from the liquid dispense device to pass through thelight curtain without causing the amplifier to generate a signal inresponse to an interrupt in a transmission of light from the pluralityof light emitters to the plurality of light detectors.

In some embodiments, a space between the plurality of light emitters andthe plurality of light detectors is large enough to accommodate a targetplate. In some embodiments, the system further comprises a conveyorconfigured to position a target plate (a) between (i) the plurality oflight emitters and (ii) the plurality of light detectors and (b) below(i) the liquid dispense device and (ii) the light curtain, such thatliquid dispensed from the liquid dispense device will travel through thelight curtain and fall onto the target plate. In some embodiments, thelight curtain is at an orthogonal angle relative to a travel directionof the conveyor. In some embodiments, the light curtain is at anon-orthogonal angle relative to a travel direction of the conveyor.

In some embodiments, the system further comprises a latching circuitcommunicatively coupled to the amplifier, wherein the latching circuitretains confirmation that an interrupt in a transmission of light fromthe plurality of light emitters to the plurality of light detectorsoccurred. In some embodiments, the latching circuit is only on duringtime intervals beginning prior to a liquid being dispensed from theliquid dispense device and ending after the liquid has been dispensed.In some embodiments, the system further comprises one or more processorsconfigured to: verify a positive dispense by reading data stored in thelatching circuit; and deactivate the latching circuit after a positivedispense has been verified.

Another aspect of the present disclosure relates to a method forpositive dispense verification, the method comprising: providing a lightcurtain by transmitting light from a plurality of light emitters towarda plurality of light detectors; positioning a target plate below thelight curtain; positioning a liquid dispense device above the targetplate and the light curtain; dispensing a liquid from the liquiddispense device onto the target plate, wherein the dispensed liquidtravels through the light curtain; and generating a signal in responseto an interrupt in a transmission of light from the plurality of lightemitters to the plurality of light detectors caused by the travel of thedispensed liquid through the light curtain.

In some embodiments, the target plate is positioned below the lightcurtain and within a distance between the plurality of light emittersand the plurality of light detectors. In some embodiments, the liquiddispense device is also positioned such that a space between the liquiddispense device and the light curtain is such that a drop of liquidhaving a volume of at least ten microliters will span the space. In someembodiments, a signal is generated if a droplet of at least threemicroliters of liquid is dispensed from the liquid dispense device. Insome embodiments, the light curtain has no gaps that would allow adroplet of three or more microliters of liquid to be dispensed from theliquid dispense device onto the target plate without interrupting atransmission of at least some light of the light curtain.

In some embodiments, the method further comprises storing dataindicating an interrupt in a transmission of light from the plurality oflight emitters to the plurality of light detectors occurred when asignal is generated. In some embodiments, the data indicating aninterrupt in a transmission of light from the plurality of lightemitters to the plurality of light detectors occurred is stored in alatching circuit. In some embodiments, the method further comprisesturning on the latching circuit before a liquid is dispensed from theliquid dispense device; and turning off the latching circuit after dataindicating an interrupt in a transmission of light from the plurality oflight emitters to the plurality of light detectors occurred is stored inthe latching circuit. In some embodiments, the method further comprisesverifying a positive dispense by reading data stored in the latchingcircuit.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a top view of a positive dispense verification systemaccording to one embodiment.

FIG. 2A is a side view of the embodiment shown in FIG. 1 .

FIG. 2B is a partial section view of the positive dispense verificationemitter shown in FIG. 2A.

FIG. 2C is a partial section view of the positive dispense verificationreceiver shown in FIG. 2A.

DETAILED DESCRIPTION

Embodiments of the present disclosure are described in detail withreference to the drawing figures wherein like reference numeralsidentify similar or identical elements. It is to be understood that thedisclosed embodiments are merely examples of the disclosure, which maybe embodied in various forms. Well-known functions or constructions arenot described in detail to avoid obscuring the present disclosure inunnecessary detail. Therefore, specific structural and functionaldetails disclosed herein are not to be interpreted as limiting, butmerely as a basis for the claims and as a representative basis forteaching one skilled in the art to variously employ the presentdisclosure in virtually any appropriately detailed structure.

The present invention relates to systems and methods for verifying whena dispensing device, such as a pipette, has successfully dispensed asample into a container or slide. This is also referred to as positivedispense verification or “PDV.” Samples as referred to herein areliquid, but it is contemplated that samples can also be solid. Systemsand methods described herein are described in the context of samplesused for microbiological testing including procedures for inoculating agrowth medium with a sample. However, such description is non-limitingand it is contemplated that the systems and methods described can beused in any context where accurate positive dispense verification ofmaterial, e.g., liquid, is desired.

In one aspect, the present invention relates to a system for PDV. FIGS.1 and 2A illustrate one embodiment of a PDV system 10. System 10includes a sensor apparatus 20, a target plate 30, and an instrument 50.One exemplary instrument 50 of system 10 is InoqulA™ by Becton DickinsonKiestra™ (“BD”). When instrument 50 is InoqulA, processes forinoculating, incubating and testing samples are fully automated. InoqulAutilizes three robotic arms for the automated transport of patientsample tubes, pipettes, and any samples disposed therein, to variouslocations around the instrument. In particular, one robotic arm isconfigured to transport and dispense samples from a pipette into thetarget plate. As will be described in greater detail below, it isbetween the pipette and the target plate that samples are detected by asensor for PDV.

Returning to the elements of system 10, sensor apparatus 20 isstructurally connected to instrument 50 and includes a PDV emitter 22and a PDV receiver 24. As shown in FIGS. 1 and 2A, PDV emitter 22 ispositioned at a distance from PDV receiver 24 so that a physical spaceexists between the two. In the illustrated embodiment, the space betweenPDV emitter 22 and PDV receiver 24 comfortably accommodates a plate,such as a plate containing a growth medium. PDV emitter 22 includes asource of light disposed on an inside facing surface 23 of PDV emitter22 so that when activated, the light is received and detected by aninside facing surface 25 of PDV receiver 24. An elevation of the lightsource relative to instrument 50 at PDV emitter is approximately thesame as an elevation of the light source at PDV receiver 24 so that anaxis through each is perpendicular to the direction of gravity. As bestshown in FIGS. 1 and 2A, light travelling between PDV emitter 22 and PDVreceiver 24 creates a light curtain 26.

PDV receiver 24 includes an amplifier (not shown) configured to processa light signal so that when a momentary interrupt, i.e., a break, occursin the light received by PDV receiver 24, sensor apparatus 20 capturesthe momentary change in signal. In one example, a drop of a samplepassing through light curtain 26 causes a momentary interrupt in thelight, and the interrupt is captured by a latching circuit in oneembodiment. The latching circuit of sensor apparatus 20 is configured tolatch the signal change (disruption) due to the momentary interrupt.System 10 is further configured so that a computer (not shown) is inelectronic communication with sensor apparatus 20 for output to a userof any signal interrupts latched by the latching circuit. The operationof a processor in communication with sensor apparatus 20 is typicallyasynchronous so that the computer processor can pick up the signalchange latched by the sensor at a point in time after it occurs.Elements of system 10 function in a similar manner regardless of whethera polarity of the signal in the interrupted state is positive ornegative.

Settings of the amplifier can be adjusted to optimize the necessaryvolume of a sample drop that can be detected when passing through thelight curtain. Put another way, a threshold signal disruption that willbe latched by the circuit can be modified through the settings of theamplifier. In one example, the sensor apparatus including PDV emitterand PDV receiver is model BOHOOCJ by Balluff and the amplifier is modelBAEOONJ by Balluff. When operating per its design specification, theBalluff sensor generates a light curtain 18.5 mm wide and 5 mm in depth.

As shown in FIGS. 1 and 2A, the light source provides light sufficientso that light curtain 26 between PDV emitter 22 and PDV receiver 24 hasa width sufficient so that a positive dispense can be detected even whena pipette 52 is positioned at different locations in a directionorthogonal to a length of light curtain 26. For example, if pipette 52is moved plus or minus five millimeters in such direction, a positivedispense of a sample can still be detected. The device for providing alight source is chosen so that when activated, it produces a light witha wavelength that does not freely transmit through a clear substancesuch as water. In one example, the wavelength is close to the visiblespectrum and is between 800 and 900 nm. In another example, thewavelength is 850 nm. Although applicants do not wish to be held to aparticular theory, generating a light curtain with a wavelength between800 and 900 nm is advantageous because light in this wavelength range isabsorbed by water, i.e., transmission of these wavelengths is easilyblocked by water, yet light in this range of wavelengths is perceptiblerelative to ambient lighting. In those embodiments where samples areeither aqueous or have optical properties similar to those of water, thewavelength for the light curtain should be tuned to the wavelengthdescribed above. If the wavelengths of the light source are not tunedproperly, the light forming the curtain may simply be transmittedthrough the falling sample without disruption, in which case the drop offalling sample will not register. The light sources are selected to havean intensity and a placement such that a sample droplet with apredetermined volume is detectable when light traveling from the PDVemitter 22 is disrupted by the droplet. Other variables that areconsidered for determining the selected intensity for the light sourcesinclude whether or not the sample is a liquid and the ambient lightingconditions.

The device used to generate light is a matter of design choice with theabove parameters as guidance. In one example, and as shown in FIG. 2B,the light source can be an array of LEDs 27. LEDs 27A-H are distributedin a row on inside face 23 of PDV emitter 22. There are eight LEDs 27A-Hin FIG. 2B, spaced approximately equidistant from one another so thatwhen light is generated, light beams from each LED 27A-H overlapcreating light curtain 26 with no gaps that would allow a droplet topass through the curtain without registering a disrupted signal. Thespace between LEDs 27A-H is equal to or less than an amount necessary toensure no such gap exists between adjacent light beams. Eight detectors28A-H are positioned in a linear array on inside face 25 of PDV receiver24, as shown in FIG. 2C, so that each detector 28A-H corresponds to anLED 27A-H. It follows that a detector array 28 has approximately thesame dimensions as LED array 27 (the combined LEDs 27A-H). In thismanner, light is transmitted from each LED 27A-H to each detector in adirection that is approximately orthogonal to the direction in which theplates pass under sensor apparatus 20. Because the direction of lightfrom each LED 27A-H is the same and each light beam at least partiallyoverlaps a light beam from an adjacent LED, a continuous light curtainis produced between PDV emitter 22 and PDV receiver 24, minimizing thepossibility that a droplet of sample may fall undetected onto the platewhen dispensed from a pipette. Through the inclusion of LEDs anddetectors into sensor apparatus 20 in the manner described above,detection of a droplet of partially optically transparent sample (e.g.,water), where the volume of the droplet is about three microliter isknown to be possible. Indeed, droplets with even smaller volumes arealso detectable and adjusting the parameters of the emitter/detector todetect such lower volume droplets is contemplated. This can beaccomplished, for example, by adjusting light intensity and a distancebetween the PDV emitter and the pipette, among other factors describedherein. There is no apparent upper limit to the volume of sample thatcan be detected.

In other examples, LEDs can be distributed over several rows or in otherpatterns. For any of the above examples, the number of LEDs in an arrayand/or the number of detectors in an array can be two, three, four,five, six, seven or even more than the eight described above.

Generally, the number of LEDs used depends on how precisely the LEDs,the light detectors and the pipette tip can be aligned. For example, ifhighly precise alignment can be achieved, then two LEDs may beappropriate. However, if precise alignment is difficult to achieve, thenmore LEDs (e.g. ten LEDs) may be the appropriate number. Althoughalignment precision may influence the number of LEDs included on the PDVemitter, other factors such as light curtain size may also influence thenumber of LEDs. Indeed, the number of LEDs on the PDV emitter may belargely a matter of design choice depending on the light curtainparameters. For example, different numbers of LEDs will provide lightcurtains having different widths (i.e., detection zones). Although thepresent invention contemplates that the LEDs may be distributed oninside surface 23 of PDV emitter 22 in a variety of patterns that differfrom the example described above, the distribution of detectors willmirror any such pattern of LEDs. In other words, any suitable pattern ofemitters and detectors will generate a substantially continuous lightcurtain sufficient to detect droplets passing therethrough when thelight source is activated. In still further examples, the number of LEDscan be greater than the number of detectors. However, as a generalmatter, the number of LEDs will typically be equal to the number ofdetectors. Although different wavelengths of light might be employed,for light curtains configured to detect drops of liquid that are wateror a liquid with optical transmittance similar to water, LEDs thatgenerate infrared light at a wavelength of 850 nm are contemplated assuitable.

System 10 also includes target plate 30. Target plate 30 has a circularbase 31 with an annular rim 32 extending distally from circular base 31.An area of circular base 31 and depth of annular rim 32 are sized sothat sufficient space exists to inoculate, incubate and test samples. Inthe illustrated embodiment, target plate 30 is sized to fit within thespace between PDV emitter 22 and PDV receiver 24. Target plate 30includes a bottom surface suited for placement on a conveyor 54 ofinstrument 50. The bottom surface of target plate 30 is generally flat.In a variant, target plate 30 can be another geometric shape, such asone with a rectangular or polygonal base. In further variants, targetplate 30 can be substituted with a broth tube or slides which would thenbe used to inoculate samples.

Instrument 50 of system 10 is shown in FIGS. 1 and 2A and includes a topsurface 51, conveyor 54 and pipette 52. Pipette 52 is connected to arobot arm (not shown) which is part of instrument 50. Of course, amechanism for securement of pipette 52 to instrument 50 and structure tofacilitate movement of pipette 52 are a matter of design choice. Forexample, and as noted above, instrument 50 can be InoqulA™ by BD, and arobotic arm of InoqulA can retrieve and transport pipette as needed forthe inoculation of a plate. In other examples, pipette can be manuallytransported to an inoculation location to dispense a sample.

FIG. 1 shows how each component of system 10 is positioned relative tothe others. Plate 30 is disposed on conveyor 54 of instrument 50. PDVemitter 22 and PDV receiver 24 of sensor apparatus 20 are connected toinstrument 50 on opposite sides of conveyor 54. In an operationalposition as best shown in FIG. 2A, pipette 52 is positioned so thatlight curtain 26, or a physical space for a light curtain, is disposedin between plate 30 and pipette 52. Sufficient space is maintainedbetween light curtain 26 and pipette 52 at all times so that a drop ofthe sample on pipette 52 will not be falsely detected. For example, if adrop of a sample is clinging to a tip 53 of pipette 52, a positiveresponse by sensor apparatus 20 will not be indicated. Thus, the LEDs oranother light source are positioned on sensor apparatus 20 so that a toplimit of light curtain 26 generated by the light source is beneath thelowest point of the largest anticipated sample drop hanging from pipettetip 53 when pipette 52 is at its lowest maneuverable position over lightcurtain 26. In this manner, there is no circumstance where a sampledroplet will contact light curtain 26 without being completely dispensedfrom pipette 52 prior to passing through light curtain 26. Consequently,the spacing is such that a droplet hanging from the pipette will not bedetected unless and until it detaches and falls from the pipette. Insome examples, the minimum distance between light curtain 26 and pipette52 tip is just enough to accommodate a ten microliter drop hanging frompipette 52.

In some embodiments, the system can include two or more sensor apparatusand two or more pipettes dispensing samples into corresponding plates.For example, the system can include two sensor apparatus each having aPDV emitter and receiver with a light curtain therebetween when the PDVemitter is activated. Each sensor apparatus can be positioned at adifferent location along the conveyor so that two or more plates on theconveyor can advance until one is under each light curtain, at whichtime a pipette is positioned above each sensor apparatus. In this way,two or more plates can be simultaneously inoculated with PDV.

In other embodiments, the PDV emitter and the PDV receiver can bepositioned so that the light curtain decreases or increases in elevationas it travels from the emitter to the receiver. Similarly, the emitterand receiver can be positioned at different locations relative to alength of the conveyor so that the light curtain is at a non-orthogonalangle relative to the length of the conveyor.

In some embodiments, sensor apparatus 20 can be configured so that atrigger indicating a positive dispense can only occur when the pipetteis proximal to sensor apparatus 20. Alternatively, sensor apparatus 20can be configured so that a positive response can only be detected whenpipette 52 is dispensed. To configure system 10 in this way, thelatching circuit is only turned on to detect a change in signal (i.e.,threshold signal disruption) for a narrow window of time fromimmediately prior to dispensing of pipette 52 until shortly thereafter.In other embodiments, sensor apparatus 20 can be configured to activateonly when pipette is dispensed and the target plate is in the correctposition on the conveyor for receiving the sample. For example, thelatching circuit is turned on for a narrow window of time commencingprior to dispense of pipette 52, and reflective optical sensor(s) (notshown) of system 10 detect whether target plate 30 is under sensorapparatus 20. In this manner, a positive dispense is only detectablewhen the latching circuit is on and the optical sensor(s) registers apositive detection of target plate 30. It is further contemplated thatthe sensor apparatus and/or instrument can be configured to recognize apositive dispense in any manner desired for a particular inoculation andtesting regime. Sensing techniques can be adapted for use in conjunctionwith any computer and are not limiting in this regard. For example,latching onto a signal change is not contingent on incorporation of aparticular computer into system 10.

Advantages of the system include that it has a high degree ofreliability and positive dispense can be verified in a highly accuratemanner. For example, when positive dispense is only detected if thepipette and plate are in position, false positives can be greatlyreduced, such as those that would occur when a pipette properlydispenses, but misses the target plate below. Similarly, false negativesare mitigated because the sensor has a high degree of sensitivity. Thesystem is also cost effective and can be configured for use in small orunconventional spaces. Another advantage of the system is that it caneasily be tailored so that a light curtain generated is wide enough forany expected tolerance range for plates advancing through an instrument.In this manner, if plates do not stop at the same exact location undersensor assembly each time, light curtain will be wide enough so that nofalse negatives will occur.

In another aspect, the present invention relates to a method for PDV.Throughout the steps of the method, the light source is active and lightcurtain 26 spans between PDV emitter 22 and PDV receiver 24. In oneembodiment, plate 30 ready for inoculation (i.e., supporting a growthmedium or agar, not shown), is positioned on conveyor 54 of instrument50. If not already in position, plate 30 is advanced on conveyor 54 toan inoculation location, such as that shown in FIGS. 1 and 2A. In atleast one variant, instrument 50 includes a plate detection light sensor(not shown) at the inoculation location positioned in a manner so thatit detects when plate 30 is at a position for inoculation. Of course,other detection mechanisms can also be used to verify the position ofplate 30 on instrument 50 such as a weight sensor positioned to detectthe weight of plate 30.

At the inoculation location, a common plane passes through plate 30, PDVemitter 22 and PDV receiver 24. In other words, plate 30 is positionedso that at least part of plate 30 lies in between light curtain 26 andconveyor 54 when measured in the direction of gravity.

When pipette is ready to be dispensed, and just prior to dispense of thesample from pipette 52, the latching circuit of sensor apparatus 20 isset. With the latching circuit set, light signals from the PDV emitters22 are detected by PDV receiver 24 are monitored for any changes. Priorto this time, any changes or other interruptions in the signal receivedby PDV receiver 24 are not captured by the latching circuit, thusavoiding any false positives. The latching circuit is configured tolatch onto any changes in the digital output of the signal generated bythe light receiver and in this way operates in a binary manner. In otherwords, when light travels from PDV emitter to PDV receiveruninterrupted, a first signal based on light received is detected. Ifthe light is interrupted, then a second signal is detected. For example,uninterrupted light results in a detection of “0” while interruptedlight results in a detection of “1.”

When the sample is dispensed from pipette 52 into plate 30 (i.e. thecontainer being inoculated), a momentary interruption occurs in lightcurtain 26 spanning between PDV emitter 22 and PDV receiver 24. Thelight curtain 26 is illustrated as oriented horizontally, but otherorientations are possible. The momentary interruption is detected at PDVreceiver 24, converted into digital output by the amplifier, and thenlatched by the latching circuit. Thus, even after the interruptionceases and the signal returns to an uninterrupted state, the latchingcircuit retains confirmation that a positive dispense occurred. At anytime during this process, a command can be entered into a computerintegrated with system 10 to query as to whether a positive dispense hasoccurred. For example, a command can be entered into the computer fiveseconds after the latching circuit has latched a signal disruptionindicative of a positive dispense. The computer will seek out datastored via the latching circuit and output the data for a user. In thiscase, the computer will identify and then output that a positivedispense has occurred. At this time, the latching circuit is deactivatedand the detection window closes as the verification of positive dispenseis complete. The method can then be repeated with another sample andplate. As noted above, although the latching circuit is deactivated,light curtain may remain on at all times.

To optimize the method of using system 10 to perform PDV, many externalfactors can be controlled. For example, ambient light should becontrolled to minimize interference with the wavelength of light curtain26. Dust surrounding instrument 50 and system 10 as a whole should alsobe controlled and minimized. In addition, if plates are conveyed tosensor apparatus 20 via a conveyor, as described in some examples above,the conveyor should be tuned and otherwise checked so that it operateswith minimal vibration. This will prevent any vibrations of theconveyor, passed to plates 30, from causing plate 30 to contact lightcurtain 26, and therefore avoid false positive detections.

Although the invention herein has been described with reference toparticular embodiments, it is to be understood that these embodimentsare merely illustrative of the principles and applications of thepresent invention. It is therefore to be understood that numerousmodifications may be made to the illustrative embodiments and that otherarrangements may be devised without departing from the spirit and scopeof the present invention as defined by the appended claims.

1-17. (canceled)
 18. A method for positive dispense verification, themethod comprising: providing a light curtain by transmitting light froma plurality of light emitters toward a plurality of light detectors;positioning a target plate below the light curtain; positioning a liquiddispense device above the target plate and the light curtain; dispensinga liquid from the liquid dispense device onto the target plate, whereinthe dispensed liquid travels through the light curtain; and generating asignal in response to an interrupt in a transmission of light from theplurality of light emitters to the plurality of light detectors causedby the travel of the dispensed liquid through the light curtain.
 19. Themethod of claim 18, wherein the target plate is positioned below thelight curtain and within a distance between the plurality of lightemitters and the plurality of light detectors.
 20. The method of claim18, wherein the liquid dispense device is also positioned such that aspace between the liquid dispense device and the light curtain is suchthat a drop of liquid having a volume of at least ten microliters willspan the space.
 21. The method of claim 18, wherein a signal isgenerated if a droplet of at least three microliters of liquid isdispensed from the liquid dispense device.
 22. The method of claim 18,wherein the light curtain has no gaps that would allow a droplet ofthree or more microliters of liquid to be dispensed from the liquiddispense device onto the target plate without interrupting atransmission of at least some light of the light curtain.
 23. The methodof claim 18 further comprising: storing data indicating an interrupt ina transmission of light from the plurality of light emitters to theplurality of light detectors occurs when a signal is generated.
 24. Themethod of claim 23, wherein the data indicating an interrupt in atransmission of light from the plurality of light emitters to theplurality of light detectors has occurred is stored in a latchingcircuit.
 25. The method of claim 24 further comprising: turning on thelatching circuit before a liquid is dispensed from the liquid dispensedevice; turning off the latching circuit after data indicating aninterrupt in a transmission of light from the plurality of lightemitters to the plurality of light detectors occurred is stored in thelatching circuit; and verifying a positive dispense by reading datastored in the latching circuit.
 26. (canceled)